Infections with opportunistic and pathogenic fungi represent an emerging and widespread public health problem in normal hosts and in those with immune systems compromised by AIDS, cancer, and immune-suppressive therapy. Pathogenic mechanisms by which fungi establish themselves in the host, and immune mechanisms by which the host recognizes and destroys fungi are poorly understood. The research goal of this application is to investigate the molecular basis of these host-fungal pathogen interactions. WI-1, a 120kd surface protein on B. dermatitidis yeasts, will serve as the linchpin for the project. Studies will address the role of WI-1 in promoting fungal adherence, invasion, and escape from innate host-defense mechanisms. This project is integrated into already ongoing studies that investigate T-lymphocyte recognition of WI-1 as a mechanism of immune-mediated destruction of B. dermatitidis. Together, they offer a comprehensive program for understanding the molecular pathogenesis and immunobiology of fungal infection. The proposed project will utilize contemporary cellular, molecular and genetic techniques to study early events in microbial pathogenesis. An in vitro experimental system in which to dissect these events has been developed by the candidate. Initial research projects will involve assays to measure B. dermatitidis binding and invasion of the basement membrane and to dissect the roles of WI-1 and individual membrane components laminin, nidogen, heparin sulfate proteoglycan, and collagen IV in promoting this interaction. Subsequent experiments will investigate the role of surface WI-1 in dictating interactions with CD14 and CD18 receptors on human macrophages and other phagocytes that constitute the innate inflammatory response to the fungus. Genetically related wild-type, attenuated, and avirulent strains with defined alterations in WI-1 expression will be used to assess the role of masking and shedding of WI-1 as a mechanism of escape from recognition and killing mediated by these cells. Later in the award period, WI-1 domains that mediate binding to cell receptors and basement membrane components will be mapped using immunological and molecular techniques. The project will be pursued in a strong research environment, which offers the collaborative guidance of established experts needed for the candidate's career development and completion of the proposed work. Results from this work will establish a paradigm for understanding the molecular basis of pivotal steps by which B. dermatitidis and related fungi initiate infection and escape immune surveillance. This may lead directly to new avenues for preventing and treating infections with medically important fungi.